Observations of the magnetohydrodynamic dynamo effect in a spheromak plasma

al-Karkhy, A; Browning, Philippa; Cunningham, G.; Gee, S J; Rusbridge, M G

doi:10.1103/physrevlett.70.1814

Cited by 66 publications

(47 citation statements)

References 11 publications

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“…6 However, it was not until recently 7 that the direct observation of the dynamo electric field has been attempted by measuring ṽ and B simultaneously, followed by other experiments. [8][9][10] In this paper, we report the results obtained by a series of the detailed experiments 7,11,12 conducted in three RFP devices. MHD dynamo has been observed in low collisionality region while a new ''diamagnetic dynamo'' has been observed in the high collisionality region.…”

Section: ͑1͒mentioning

confidence: 99%

Measurement of the dynamo effect in a plasma

Prager

Almagri

et al. 1996

Physics of Plasmas

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A series of detailed experiments has been conducted in three laboratory plasma devices to measure the dynamo electric field along the equilibrium field line ͑the ␣ effect͒ arising from the correlation between the fluctuating flow velocity and magnetic field. The fluctuating flow velocity is obtained from probe measurement of the fluctuating E؋B drift and electron diamagnetic drift. The three major findings are the following: ͑1͒ The ␣ effect accounts for the dynamo current generation, even in the time dependence through a ''sawtooth'' cycle; ͑2͒ at low collisionality the dynamo is explained primarily by the widely studied pressureless magnetohydrodynamic ͑MHD͒ model, i.e., the fluctuating velocity is dominated by the E؋B drift; ͑3͒ at high collisionality, a new ''diamagnetic dynamo'' is observed, in which the fluctuating velocity is dominated by the electron diamagnetic drift. In addition, direct measurements of the helicity flux indicate that the dynamo activity transports magnetic helicity from one part of the plasma to another, but the total helicity is roughly conserved, verifying Taylor's ͓Phys. Rev. Lett. 33, 1139 ͑1974͒; Rev. Mod. Phys. 58, 741 ͑1986͔͒ conjecture.

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Section: ͑1͒mentioning

confidence: 99%

Measurement of the dynamo effect in a plasma

Prager

Almagri

et al. 1996

Physics of Plasmas

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“…Applying a second, long current pulse (sustainment pulse) at currents below a formation threshold, 13 as in many SSPX discharges, 2,14,15 improves performance by delaying the onset of MHD modes that are resonant in the closed-flux region, 6 and higher toroidal-current increases magnetic fields, and larger volumes of closed flux can be achieved. 16 The simulations reveal the sensitivity of the magnetic surfaces and the energy confinement with respect to IV.…”

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NIMROD resistive magnetohydrodynamic simulations of spheromak physics

et al. 2008

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“…Correlations were measured between fluctuations of E and B to study the MHD dynamo on SPHEX [45]. A dynamo electric field was constructed as E+ = Ii x bi = fiI l B, /B which can drive toroidal current in a relaxed spheromak (even though Eext = 0).…”

Section: Appendix 2 Recent Results From the Sphex Experimentsmentioning

confidence: 99%

The Spheromak path to fusion energy

Hooper¹,

Barnes²,

Bellan³

1998

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The spheromak is a simple and robust magnetofluid configuration with several attractive reactor attributes including compact geometry, no material center post, high engineering p, and sustained steady state operation through helicity injection. Spheromak physics was extensively studied in the US program and abroad (especially Japan) in the 1980's with work continuing into the 1990s in Japan and the UK. Scientific results included demonstration of self-organization at constant helicity, control of the tilt and shift modes by shaped flux conservers, elucidation of the role of magnetic reconnection in the magnetic dynamo, and sustainment of a spheromak by helicity injection.Several groups attained electron temperatures above 100 eV in decaying plasmas, with CTX reaching 400 eV. This experiment had high magnetic field (>l T on the edge and -3 T near the symmetry axis) and good confinement. More recently, analysis of CTX found the energy confinement in the plasma core to be consistent with Rechester-Rosenbluth transport in a fluctuating magnetic field, potentially scaling to good confinement at higher electron temperatures. The SPHEX group developed an understanding of the dynamo in sustained spheromaks but in a relatively cold device. These and other physics results provide a foundation for a new "concept exploration" experiment to study the physics of a hot, sustained spheromak.If successful, this work leads to a next generation, proof-of-principle program.The new SSPX experiment will address the physics of a large-scale sustained spheromak in a national laboratory (LLNL) setting. The key issue in near term spheromak research will be to explore the possibly deleterious effects of sustainment on confinement.Other important issues include exploring the P scaling of confinement, scaling with Lundquist number S, and determining the need for active current-profile control. Collaborators from universities and other national laboratories are contributing experience from previous work, diagnostics, and physics support. Experiments at PPPL and Swarthmore are being conducted on the physics of magnetic reconnection, yielding physics results which should help advance the confinement work.A spheromak reactor will require steady state operation with the equilibrium fully supported by external coils. Although the present generation of experiments can provide data on the initial stages of the transition from short-pulsed operation, sustainment longer than the wall resistance time will be addressed in the proof-of-principle experiments.-lContents

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Observations of the magnetohydrodynamic dynamo effect in a spheromak plasma

Cited by 66 publications

References 11 publications

Measurement of the dynamo effect in a plasma

Measurement of the dynamo effect in a plasma

NIMROD resistive magnetohydrodynamic simulations of spheromak physics

The Spheromak path to fusion energy

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